Never put anything in a BUG_ON that would lead to incorrect code if BUG_ON were
modified to be a no-op.  So, in

	BUG_ON(expression)

expression should never have side-effects.

Some modules have traditionally put all the EXPORT_SYMBOL()'s together in a
single file.  But lately people seem to prefer to locate them in the same place
as the function definition; this has the benefit that you're less likely to
allow the function and the export to get out of sync.